Distribution: Occurring on both sides of the Cascades crest in Washington; widespread in the eastern half of North America; Eurasia.
Habitat: Shallow, quiet to slow-moving water.
Origin: Introduced from Europe and/or eastern North America
Conservation Status: Not of concern
Monoecious, perennial herbs of wet places from extensive rhizomes, the stems up to 1.5 m. tall, erect, cylindrical and pithy.
Leaves alternate, sheathing, linear, the blades 3-10 mm. broad, deep green, convex on the outer surface.
Flowers naked in terminal, cylindrical, spike-like inflorescences, the staminate above the pistillate, the two portions separated by 0.5-4 cm.; staminate flowers consisting of 2-5 stamens borne directly on the main axis, intermixed with slender hairs; pistillate flowers a single, 1-celled pistil, subtended by a linear bract dilated at the tip; pistillate section up to 15 mm. thick, brown; abortive ovaries flattened, wedge-shaped.
Fruit dry, 1 mm. long, ellipsoid.